Fire extinguishing powder composition



United States Patent 3,523,893 FIRE EXTINGUISHING POWDER COMPOSITIONZbigniew J. Lobos, East Brunswick, N .J., assignor to Stop-Fire, Inc.,Monmouth Junction, NJ. No Drawing. Filed Mar. 22, 1967, Ser. No. 625,034Int. Cl. A62d 1/00 US. Cl. 252-5 4 Claims ABSTRACT OF THE DISCLOSURE Adry composition of ammonium phosphate-base fire extinguishing powderwith finely divided boron oxide in admixture therewith and the processof making the same.

The present invention relates to ammonium phosphatebase fireextinguishing powders, more particularly, to the drying of such powderschemically when the ingredients are being mixed together.

Ammonium phosphate-base fire extinguishing powders are generallyreferred to as A, B, C since these powders are useful in combating alltypes of fires which are known as class A, B, and class C fires.However, these ammonium phosphate-base fire extinguishing powders, likemany other substances, have the harmful property of picking up moisturefrom the atmosphere up to the point of saturation at given relativehumidity and temperature. It has been found that in one generally usedtype of such a fire extinguishing powder the moisture content of thepowder rapidly increases above 60 percent of the relative humidity ofthe atmosphere and reaches 4.0 percent at 90 percent of the relativehumidity. Carefully controlled tests have produced the following resultswith respect to the moisture content in the powder at different relativehumidities of the atmosphere:

Relative humidity of the air, Moisture contents in the percent: powder,percent 0.022

The particular fire extinguishing powder used in the above tests has thefollowing composition:

Parts by weight,

percent Monoammonium phosphate 91.85 Tricalcium phosphate precipitated5.00 Silica (300 mesh particles) 0.45

It is pointed out that because during production the powder is incontact with the surrounding atmosphere for a relatively short period oftime, the actual values for the moisture in the production powder arenot quite as high as the point of saturation ascertained in thelaboratory for different relative humidities. At relative humidities ofabout -90 percent, it was noted that in several production runs themoisture contents were only up to about 0.3 percent.

The presence of moisture in dry chemical fire eX- tinguishing powders isextremely troublesome for a number of reasons. The moisture is mainlyresponsible for caking of the powder thus adversely affecting thefree-flowing of the powder and the rate of dispersion on a fire. Thus,the extinguishing eifect of such a fire extinguishing powder issignificantly lower. Moisture also lowers the bulk Amino-acetic acid(glycine) (200 mesh particles) Silicone 'ice density of the powder and,as a result, a greater volume of powder is required for the fireextinguisher. For example, an A, B, C powder with 0.01 percent of thmoisture has 10 percent less volume than the same weight of the powderwith 0.23 percent of moisture.

Any suitable silicon may be used, such as dimethyldiethoxysilane,partially hydrolyzed methylhydrogen polysiloxanes, ororganopolysiloxanes.

A major disadvantage of moisture in fire extinguishing powders is thatmoisture lowers the electrical resistance of the powder, thus making thepowder useless for extinguishing electrical fires. The following data,which was found experimentally, will illustrate the affect of moistureon electrical resistance of the powder:

Electrical resistance Moisture percentage: in megohms 0.020 10,000,0000.048 950,000 0.083 300,000 0.105 23,000 0.140 9,500

There are two sources of the moisture content in A, B, C powders. Onesource is the moisture already present in the ammonium phosphate and inthe other ingredients, but mostly in the tricalcium phosphate. Secondly,moisture is picked up from the humid atmosphere during the production ofthe powder. During the production operation the greatest quantity ofmoisture is picked up from the atmosphere during the sifting operationand during the vacuum air conveying of the powder. It will at once beapparent that in both of these operations the powder is in short butdirect contact with the huge volume of the moist atmosphere. Further,the finer the powder the larger will be the surface area exposed to theatmosphere and, accordingly, the greater will be the absorption of themoisture from the atmosphere.

In order to produce an A, B, C fire extinguishing powder of good qualityit is of prime importance to remove the moisture from the powder. Up tothe present time, there were two possible approaches of removing themoisture from the powder. These approaches may be summarized as follows:

(1) Dehumidifying the atmosphere in the powder production department tolower the relative humidity of the atmosphere to about 40 percent; and

(2) Drying the mixed powders.

The first approach is not satisfactory because of the ingredientsthemselves are partly responsible for the moisture content of thepowder. Thus, controlling the atmosphere alone would only partiallyremove moisture from the powder.

The drying of the fire extinguishing powder is preferably accomplishedby passing the powder through a heated oven or by heating the powder ina jacketed mixer and then removing the moist air by means of a vacuumpump.

It is clearly apparent that the foregoing methods of drying requireexpensive installations of equipments, require additional space in theproduction department, increase the time of a production run and hencedecrease the total production of powder, and the costs of production aresubstantially increased while only a small quantity of moisture isactually removed from the powder. The quantity of moisture actuallyremoved may represerit only a small fraction of 1 percent.

It is therefore a principal object of the present invention to provide anovel and improved composition of dry ammonium phosphate-base fireextinguishing powder.

It is another object of the present invention to provide an extremelyinexpensive, simple but very convenient chemical process for dryingammonium phosphate-base fire extinguishing powders without requiring anyadditional installations.

It is a further object of the present invention to provide a novel andimproved chemical fire extinguishing powder having an ammonium phosphatebase and wherein the moisture is removed chemically.

In one aspect of the present invention the foregoing objects areachieved and the above-mentioned disadvantages are eliminated by a dryammonium phosphate-base fire extinguishing powder composition accordingto the present invention. According to the present invention, theingredients of an ammonium phosphate-base fire extinguishing powder aremixed together. Boron oxide as a drying agent is then mixed to the batchof powder as the last or next to the last ingredient. In some instancesthe boron oxide may be mixed with the ingredients of the powder after aliquid silicone as a polymerization agent has been added. The time ofthe moisture removal from the fire extinguishing powder depends upon thefineness and quantity of the boron oxide added. The greater the quantityand the finer the boron oxide the shorter will be the time ofdehydration. The entire process is performed at room temperature.

Other objects and advantages of the present invention will be apparentto those skilled in the art from the following description.

According to the present invention boron oxide (B is used as the dryingagent for an A, B, C powder. The boron oxide reacts with water withformation of boric acid in accordance with the following formula:

The boron oxide is added as the last ingredient to every batch of theammonium phosphate base A, B, C fire extinguishing powder. The quantityof the boron oxide which is added to a particular batch will depend uponthe quantity of the moisture in that batch of powder. The moisture inthe powder, in turn, will largely depend upon the humidity of theatmosphere. In general, 0.2 percent parts by weight of boron oxide willbe added during a dry day and up to 0.6 percent parts by weight will beadded in the days with a high relative humidity. The time for theremoval of the moisture from the batch of powder will depend upon thefineness and quantity of the boron oxide added.

In order to enable the polymerization to proceed of the liquid siliconeused as an ingredient for the A, B, C powder some water content isnecessary. Therefore, a small quantity of moisture must remain withinthe powder or the time of the polymerization of the silicone must beshorter than the time for the removal of the moisture. The quantity ofmoisture may be regulated by controlling the quantity of the boron oxideadded. The time of the moisture removal can be regulated by con trollingboth the quantity and finess of the boron oxide powder. It should beborne in mind that the time for polymerization of the silicone isconsiderably shorter than the time required to remove the moisture fromthe powder.

Typical mixtures wherein moisture is removed from ammoniumphosphate-base fire extinguishing powders according to the presentinvention are given in the following examples, the parts being byweight:

EXAMPLE I 91.85 percent of monoammonium phosphate, 5.00 percent oftricalcium phosphate precipitated, 0.45 percent of silica and 2.00percent of amino-acetic acid are mixed together at room temperature in aglass jar. The total quantity of the powder is 200 grams. The mixturecontains 0.234 percent of moisture. After mixing of the foregoingingredients, 0.6 percent of boron oxide 120 mesh screened was mixed withthe mixture. Then, 0.5 percent of a silicone (dimethyldiethoxysilane)was added to the mixture. After 24 hours the sample was examined with amoisture analyzer and the moisture content was discovered to be 0.068percent. After one week the moisture content was noted to be 0.016percent.

EXAMPLE II A similar sample of fire extinguishing powder as set forth inExample I and having a moisture content 0.234 percent was mixed with 1.0percent of boron oxide and then 0.5 percent of the silicone was added.After 24 hours the moisture content was 0.033 percent and after one Weekthe moisture content was noted to be 0.010

percent.

EXAMPLE III 700 lbs. of the fire extinguishing powder according toExample I and containing 0.100 percent moisture was mixed with 3 lbs. ofboron oxide and then 0.5 percent of the silicone added and the entirecontents mixed. After 24 hours the moisture contents dropped to 0.016percent and after a week the moisture content was found to be only 0.002percent. It is pointed out that in this example, 2 lbs. of the boronoxide would be sufiicient to achieve virtually the same result.

In Example III, the ingredients including the boron oxide were mixed ina liquid-solid V-blender.

As pointed out above, the boron oxide reacts with the water to changeinto boric acid which is a mild antiseptic.

In all three examples, boron oxide of 120 mesh was used. However, sinceboron oxide of mesh is commerically available it is preferred to useboron oxide of this fineness. 100 mesh boron oxide reacts rather slowlyWith the fire extinguishing powder and accordingly it is possible to addmore than the calculated quantity of every batch of the powder. Theexcess boron oxide will protect the fire extinguishing powder againstmoisture for a period of several days in the event the container of thepowder is accidentally opened and relative humidity of the surroundingatmosphere is high.

Dow Corning liquid silicone 1107 is used in the fire extinguishingpowders of the above three examples. This silicone is methyl andhydrogen polysiloxane which in the presence of the moisture and asuitable catalyst generates hydrogen gas and polymerizes intolong-chained solid polymer which forms an anti-caking and waterrepelling coat around each particle of the powder. The catalysts whichmay be used for the polymerization of the silicone are those shown inU.S. Pat. 3,179,589 issued Apr. 20, 1965.

Other typical compositions of ammonium phosphatebase fire extinguishingpowders to which boron oxide may be added in accordance with the presentinvention are as follows:

Boron oxide may be added to all fire extinguishing powders to remove themoisture therefrom except those which contain carbonates or bicarbonatesof ammonium or alkali metals. Thus, boron oxide may also be used withfire extinguishing powders for light metal fires which contain mostlysodium chloride or graphite as the main ingredients. At the present timeonly ammonium phosphates are used as the main ingredients of all A, B, Cfire extinguishing powders.

Thus it can be seen that the present invention discloses an extremelysimple chemical process for removing moisture from ammoniumphosphate-base fire extinguishing powders. The moisture is removed bythe simple step of mixing boron oxide powder into a mixture of theingredients of the fire extinguishing powder. The presence of the boronoxide in the fire extinguishing powder causes a reaction with the Waterto form boric acid which in itself is an eflective fire extinguishingagent. The composition of this invention is a dry fire extinguishingpowder which will remain dry for a period of time even after itscontainer is opened to the atmosphere.

What is claimed is:

1. A dry fire extinguishing powder consisting essentially of 59-93%monoammonium phosphate, 0.2-1% boron oxide, and the remainder a memberselected from the group consisting of silica, mica, barium sulfate, mag-UNITED STATES PATENTS 2,550,113 4/1951 Flowers 252-68 XR 3,048,4708/1962 Mannhein et a1. 252385 XR 3,172,852 3/1965 Lobos 2525 3,214,37210/ 1965 Lobos 2525 MAYER WEINBLATT, Primary Examiner U.S. Cl. X.R.

